1. Molar Mass, Moles, and Molecules 7.3 Using Chemical Formulas

2. What is a Mole?  A mole is a number used to describe a quantity of something, usually referring to mass, volume, or the number of particles.  As a unit, it is shortened to mol

3. Molar Mass  The atomic mass of an element on the periodic table is the mass of 1 mole of that element (also called the molar mass, measured in g/mol).  In a chemical formula, the subscript represents how many moles of that element are present in that compound.  Multiply the number of moles by the atomic mass to find the mass of an element in a compound.  Add together the masses of all elements in the compound to find the formula mass.

4. Formula Mass Examples 1. NaCl = 2. H 2 O = 3. CaSO 4 = Complete the practice problem on page 238.

5. Converting with Molar Mass  It is possible to find the number of moles of a given formula mass by dividing by the molar mass of each element in a formula.  Ex: How many moles of CO 2 are in 88.02 g?  C =, O 2 =  Complete practice problem #1 and 3 on page 240.

6. Molecules  The quantity of a mole can also be used to find the number of particles of a substance are present (usually measured in molecules or atoms)  1 mole = 6.022 x 10 23 particles  This constant is known as Avogadro’s number.

7. Converting with Molecules  To find the number of molecules, multiply the number of moles by Avogadro’s number.  Ex: 1 mole of O 2 = ? Molecules  To find the number of moles, divide by Avogadro’s number.  Ex. 1.204x10 24 molecules of O 2 = ? Moles  Complete practice problem #2 on page 242.

8. Mass, Moles, and Molecules  To convert between all three quantities, you must go through moles. (1 st divide, then multiply)  Ex: 4.04 g of H 2 = ? Molecules of H 2  Complete practice problem #2 on page 242.

9. Exit Ticket  P. 244 - Complete #1-4 on the section review